Cyanine dyes



p 1950 J. c. FIRESTINE 2,521,705

CYANINE DYES Filed Aug. 21, 1946 SILVER BROMIDE EMULSION SILVER CHLORIDE EMULSION Patented Sept. 12, 1950 CYANINE DYES John Charles Firestine, South River, N. 1., as-

signor to E. I. du Pont de N emours & Company, Wilmington, Del., a corporation of Delaware Application August 21, 1946, SerialNo. 692,126

5 Claims.

This invention relates to the preparation of new oxazoles. More particularly, it relates to the preparation of 2-methyl 5-b'en-zoyl' benzoxazole and its cyclammonium salts andto the. preparation of cyanine'dyes therefrom; .It further pertains to silver halide emulsions containing such dyes.

An object of this invention is to provide new and'us'eful oxazole compounds. A further object is to providesuch compounds which contain a reactive methyl group in the alpha position to the heterocyclic nitrogen atoms. A still further object is to provide a new class of oxazole cyclammonium salts. which are capable of entering into cyanine dye condensation reactions. Another object is to provide a new class of cyanine dyes which confer an extra range of'spectral sensitivity to photographic silver halide emulsions. Yet another-object istoprovide photographic silver halide emulsions with'an extra range-of'spectral sensitivity. Still other objects will be apparent from the following'description of the invention.

It has been found that" 2-methyl-5-benzoyl benzoxazole can be prepared ina practical manner by reacting p-hydroxy-benzophenonedissolved in a solvent with nitric acid to'yiel'dmnitro-p-hydroxybenzophenone. The latter compound can then readily be reduced by means of powdered metal in acid: solution. to the corresponding amino compound which: can be simultaneously" or subsequently condensed with acetic anhydride to yield 2-methyl-5-benzoyl benzoxazole which has the structural formula:

. 2 wherein R' is an alkyl or aralkyl radical, e.-g-.', methyl and ethyl and benzyl, andXrepresentsthe negative radical of an acid, e. g., Cl, Br, I, SO4CH3, C104, SOsC6H5CI-I3, etc.

The compounds of Formula 2 have been found to react similarly to 2-methyl benzthiazole quaternary salts with other reactive heterocyclic nitrogen salts to form various monoand polymetlrln'e dyes. The bases can be simultaneously reacted with alkyl salts and condensed to form a 'cyanine dye if desired. However, the stepwise method is, in general, preferable to the simultaneous salt formation and dye condensation reaction.

A preferred aspect of the invention is concerned with the preparation of carbocyanine dyes in cluding those which contain substitutedmethine groups and the symmetrical and unsymmetrical types. When the symmetrical type are desired, two molecules of 2-methyl-5-benzoylbenzoiiazole quaternary salt are reacted with one mol of an ortho ester of a carboXylic-acid. In addition,.un-' symmetrical carbocyanine dyes containing arben zoyl'benzoxazole radical can be made'bya process similar to that described in United States Patents 2,071,898 and 2,0?1,899.

The ortho esters useful'in accordance withthe above teachings may be simple or mixed and of aliphatic, cycloaliphatic or aromatic carboxylic acids, including aromatic substituted aliphatic acids and aliphatic substituted aromatic acids. The ortho esters of the'carboxylic acids result in carbocyanine dyes which comprise two to three heterocyclic nitrogen nuclei, at least one of which is a S-benzoyl benzoxazoleradical bridgedlbyra trimethenyl radical CH=CHCH= or.--by,- a substitutedtrimethenylradical of the formulawherein A is a hydrocarbon radical. of the ortho esters of aliphatic carboxylic acids having more than two carbon atoms in the acid molecule, A is an alkyl radical. When an ortho ester off an aromatic carboxylic acid is used, A is an aryl radical. When orthoformic acid esters are used, however, the central hydrogen atom may be replaced by heterocyclic nuclei.

Cyanine dyes which are bridged by a mono meth'enyl radical (CH=) may be preparedx'b'y another embodiment of the invention by'reactin'g a 2-methyl5-benzoyl benzoxazole quaternary salt with a heterocyclic nitrogen compound of the type used in the preparation of cyanine dyes having a reactive thioether or selenoether group in an alpha or gamma position to a heterocyclic nitrogen atom or a reactive methyl or methylene In the case r p in such positionsh p unds i was '75 grams of yellow sparkling crystals having clude the quaternary salts of the thioethers and a melting point of 94-945 C.

selenoethers of substituted and unsubstituted thiazoles, thiazolines, oxazoles, oxazolines, selen- (b) g g igg i azoles, selenazolines, pyridines, quinolines, indol- 5 enines, diazines, e. g., pyrimidines, thiadiazoles, Seventy-nine grams of the crystalline product and quinazolines and the corresponding polyobtained by nitration of p-hydroxybenzophenone cyclic compounds, such as benzthiazoles, naphin acetic acid was dissolved in 1000 cc. of acetic thazole and anthrathiazole. anhydride and heated to reflux. The heat The cyanine dyes may be incorporated with 10 source was then removed and the compound recolloid-silver halide emulsions of various types duced by adding 150 grams of zinc dust in small including silver chloride, silver bromide, silver portions. The reaction was violent and the addichlorobromide, silver iodobromide simple and tions were regulated accordingly. After the zinc mixed emulsions. Various types of colloids can had been added, the solution was refluxed for one be used to bind the light-sensitive silver salts, hour longer and filtered from solid material. e. g., gelatin, albumin, agar agar, hydrophilic The filtrate was distilled up to 140 C. at 760 mm. cellulose acetate, hydrophilic polyamides, the pressure to remove excess acetic anhydride and interpolymers of 2,397,866, etc. The dyes may then at 14 mm. to collect the product. Z-methylbe added to the emulsions in the form of solu- 5-benzoyl benzoxazole distilled from 218-230 tions. Suitable solvents are the alcohols, for C./14 mm. as a clear viscous oil that solidified on instance methyl or ethyl alcohol, which may be cooling. It melted 103-1035 C. The yield was anhydrous or diluted with water. The dyes can 39 grams.

EXAMPLE l1 be added to the emulsion during any stage of its 2-methyl-5-benzoyl benzoxazole (2.37 grams) production; however, they are preferably added 35 was heated with diethyl sulphate (1.54 grams) at to the finished emulsion before casting. They 1 014 C. for wo hours. The melt was cooled may be incorporated in the emulsion by coating and treated with cc. of pyridine and 3 cc. of or bathing the finished photographic layer in ethyl orthoformate. The resulting solution was bath i which th dye i di l d, The quantity heated to reflux for half an hour during which may vary widely from 15 to milligram per kilo fi an Orange @0101 developed- The hot $0111 f fl able emu1sion containing about 9% galation was treated with an excess of a saturated tin, f silver halide and the rest Water aqueous solution of potassium iodide and cooled. being a practical range f quantities The red crystals that formed were filtered,

The invention will be further illustrated by the washed with water and alcohol, and crystallized following examples. The parts are all by weight. twice f alcohol' The yield was gram of glistening red needles.

EXAMPLE I This dye when added to a gelatin silver iodo- Th f h d b h bromide emulsion extended the sensitivity to a e m m um 0 y enzop emme about 5600 A. with a peak at 5400 A. The specro Ninety grams of p-hydroxybenzophenone was tral curve 15 set forth in Figure 1A of the drawdissolved in 150 cc. of glacial acetic acid and When added o a gelatin S v C or de warmed to C. Sixty grams of fuming nitric emulsion, it was found to extend the sensitivity acid was then added dropwise at such a rate that to 5720 A. with a broad peak at 5300 A. The the temperature lay between 45-50 C. When spectral curve is shown in Figure 1B of the three-fourths of the nitric acid had been added, drawing.

EXAMPLE III 3-3 diethyl, 9 methyl, 5-5' dz'benzoyl org/carbocyanz'ne iodide the nitro product crystallized and it was neces- This dye was prepared by using the same prosary to dilute the solution with another 100 cc. cedures and quantities used in the preparation of of acetic acid. When the nitric acid was comthe dye of Example II. "Ethyl orthoacetate was pletely added, the solution was stirred one-half substituted, however, in equal quantity for ethyl hour longer and then poured into 3-4 volumes orthoformate. The dye was obtained at first as of cold water. The crystals were filtered, washed an oil from the reaction mixture but after puriwell with water and recrystallized from alcohol. fication with alcohol-ether solutions, it was con- The yield of m-nitro-p-hydroxybenzophenone verted to a red powder weighing 0.02 gram.

(L lsHs This dye was made in a similar manner to Example III except that ethylorthopropionate was n-caproate, methyldiethyl ortho-isocaproate, trisubstituted in equal quantity for ethylorthoacel5 methyl ortho-formate, trimethyl ortho-benzoate, tate. The dye was obtained as 0.2 gram of red trimethyl ortho-p-toluate, trimethyl ortho-gamamorphous powder. ma-phenoxy-butyrate, trimethyl ortho-phenyl- The condensations are preferably carried out acetate, trimethyl ortho valerate. in the presence of an acid binding agent or sol- As many widely different embodiments of this vent, e. g., pyridine, piperidine, fused sodium aceinvention can be made without departing from tate, tri-n-propylamine, and tri-ethanolamine, the spirit and scope thereof, it is to be understood sodium ethylate, caustic soda, etc. Additional that the invention is not to be limited except as solvents may be used, e. g., acetic anhydride with defined by the claims. sodium acetate, alcohol with alkali metal bases, What is claimed is: etc. 1. A chemical compound of the general for- As stated above, the preparation of unsymmetmula:

C-CH=O-OH=C N N 0 0 rical dyes also forms a part of this invention. By adding difierent heterocyclic nitrogen compounds of the type set forth in the penultimate paragraph preceding the examples or the corresponding alkyl compounds, e. g., having a methyl group instead of a mercapto or selenoether group, to the reaction mixtures, a number of cyanine and carbocyanine dyes may be prepared.

In place of the specific ortho esters of carboxylic acids, there may be substituted any ester of this type which is capable of reacting with the heterocyclic nitrogen compounds. Suitable esters include trimethyl ortho-propionate, methyldiethyl- R/ \X R where R. is taken from the group consisting of alkyl and aralkyl radicals, X is the negative radical of an acid and A is taken from the group consisting of hydrogen and alkyl radicals,

2. A dye having the structural formula CzHs which in crystalline form has glistening red needles.

3. The process of preparing carbocyanine dyes which comprises reacting a 2-methyl-5-benzoyl- 5. A chemical compound of the formula:

JOHN CHARLES FIRESTINE.

(References on following page) REFERENCES CITED The following references are of record in the Number Name Date 1,962,124 Brooker June 12, 1934 2,068,047 Zeh Jan. 19, 1937 2,071,898 Piggott et a1 Feb. 23, 1937 Number Name Date Piggott Feb. 23, 1937 Wilmann Mar. 30, 1937 Schneider Sept. 19, 1939 Wilson July 6, 1943 Eistert June 6, 1944 Anderson Nov. 7, 1944 Anish Feb. 18, 1947 

1. A CHEMICAL COMPOUND OF THE GENERAL FORMULA: 